This invention relates to a vacuum container for a field emission cathode device, and more particularly to a vacuum container in which field emission elements or field emission cathodes acting as an electron source are received.
It has been recently attempted to receive a number of micro-sized field emission cathodes in a vacuum container made of glass or the like to put a field emission electronic equipment in which vacuum microstructures of a size as small as microns are integrated into practice in the form of vacuum microelectronics.
Such vacuum microelectronics are directed to development of applied field emission devices such as a field emission display device of a thin flat panel structure, an image pickup device, an electron beam device for lithography or the like.
A thin flat panel display device in which field emission cathodes are incorporated is so constructed that a plurality of micro-sized or fine cold electrodes (emitters) are arranged for each of picture cells.
The fine cold electrodes proposed each are constituted by a field emission cathode having a distal end formed into an acute angle, a field emission cathode of the MIM type, an electron emission element of the surface conductive type, an electron emission element of the PN junction type or the like.
The most typical one of such devices is a field emission display (FED) having field emission cathodes incorporated therein, as disclosed in Nikkei Electronics, No. 654 Jan. 29, 1996), pp 89-98. A typical one of the field emission cathodes is a field emission cathode called the Spindt type.
Now, such a field emission cathode of the Spindt type will be described with reference to FIG. 10. More particularly, the field emission cathode includes a cathode substrate K having a number of emitter electrodes arranged thereon. SiO2 designates an insulating layer formed all over the cathode substrate K. The insulating layer is provided thereon with a gate electrode GT in the form of a film by deposition or the like. The gate electrode GT is formed with holes, through which a distal end of the emitter electrodes E is exposed, so that electrons emitted from the emitter electrodes E may be outwardly discharged.
In the field emission cathode of the Spindt type thus constructed, application of a voltage Vgk between the cathode electrode K and the gate electrode GT permits electrons to be emitted from the distal end of the emitter electrodes E. The electrons thus emitted are captured by an anode voltage Va applied to an anode electrode A arranged opposite to the cathode electrode K through a vacuum space. A plurality of such field emission cathodes are arranged in each of groups and a plurality of such gate electrodes arranged in a stripe-like manner are scanned in order, during which plural such stripe-like cathode electrodes are fed with an image signal. This results in phosphors arranged on the anode electrode emitting light, so that the field emission cathodes may function for a display device.
Now, an envelope for such a display device will be described with reference to FIGS. 11(a) and 11(b), which are a perspective view of the envelope and a side elevation view in section thereof, respectively.
In FIGS. 11(a) and 11(b), reference numeral 1 designates a glass substrate arranged on a side of an anode (hereinafter also referred to as xe2x80x9canode-side substratexe2x80x9d) and 2 is a glass substrate on a side of a cathode (hereinafter also referred to as xe2x80x9ccathode-side substratexe2x80x9d). The anode-side substrates 1 and cathode-side substrate 2 are arranged opposite to each other so as to define a space therebetween, in which field emission cathodes of a size as small as microns and anode electrodes are received while being arranged on an inner surface of the cathode-side substrate and an inner surface of the anode-side substrate in a manner to be opposite to each other, respectively.
Reference numeral 3 designates a getter substrate, which is formed on a bottom surface thereof with an evacuation hole 6a through which the envelope is evacuated at a high vacuum. 4 is a getter member generally made of a getter material of the evaporation type. Thus, the getter member is flashed at an elevated temperature to maintain a gas pressure in the envelope at a low level, after the envelope is evacuated at a high vacuum.
The cathode-side substrate 2 and anode-side substrate 1 are sealedly joined to each other while being kept spaced from each other at a microinterval as fine as from about 250 xcexcm to millimeters. Also, both substrates 1 and 2 are arranged while being kept deviated from each other. Such arrangement permits a cathode electrode lead-out section of the field emission cathode and a gate electrode lead-out section thereof to be arranged in regions of the substrates which are kept from being opposite to each other.
Also, if color display is desired, the anode-side substrate 1 may be formed so as to have a projected region, resulting in an anode lead-out section (not shown) being arranged in the projected region.
The cathode-side substrate 2 and anode-side substrate 1 are sealedly joined at a peripheral portion thereof other than the getter substrate 3 to each other by means of frit glass 5 or the like. The getter substrate 3 is set in an evacuation unit (not shown), so that gas therein is discharged through a vacuum pump.
Thus, in the vacuum envelope in which the field emission cathodes are arranged, the cathode-side substrate 2 and anode-side substrate 1 are kept spaced from each other at a microdistance, to thereby define the space therebetween. In order to keep the space at a high vacuum, the getter 4 is generally placed in a getter chamber. Then, the getter 4 is externally heated to an elevated temperature, to thereby be evaporated, so that a getter mirror may be formed all over a surface of the getter chamber. The getter mirror serves to adsorb thereon any residual gas in the envelope after evacuation of the envelope. The residual gases include gas entering the envelope and that generated from a material for the electrodes or the like.
The space defined in such a flat-type display device in the form of a vacuum container is formed into a highly small height or dimension. Such a small height of the space causes a deterioration in passage or migration of gas in the space when the space is evacuated at a high vacuum, resulting in formation of a vacuum atmosphere in the space being highly difficult or substantially impossible. A failure in satisfactory evacuation of the space or envelope causes a deterioration in emission of the field emission cathodes due to the residual gas.
Also, the amount of material for the field emission cathodes and the like present in the space of the envelope is increased relatively to the volume of the space, resulting in a length of time required for evacuating the residual gas present in the material or absorbed on a surface thereof to form a vacuum at a predetermined level or more in the envelope being highly increased, so that the evacuation operation is deteriorated in efficiency.
The present invention has been made in view of the foregoing disadvantage of the prior art.
Accordingly, it is an object of the present- invention to provide a vacuum container for a field emission cathode device which is capable of efficiently attaining evacuation of the vacuum container.
It is another object of the present invention to provide a vacuum container for a field emission cathode device which is capable of permitting an increase in durability of-the field emission cathode device.
In accordance with the present invention, a vacuum container for a field emission cathode device is provided. The vacuum container includes a first substrate made of glass, a second substrate made of glass and arranged so as to be opposite to the first substrate, a side wall arranged between the first substrate and the second substrate to space the first and second substrates from each other, to thereby form a space therebetween, an evacuation section formed with an evacuation hole through which the space is evacuated at a high vacuum and sealed after evacuation, to thereby keep the space at a vacuum, and a gas emission material arranged at at least one position including a position which is defined in the space or an additional space contiguous to the space and is-farthest from the evacuation section.
In a preferred embodiment of the present invention, the first substrate is formed thereon with field emission cathodes and the second substrate is provided thereon with anodes, which are arranged in a manner to be opposite to the field emission cathodes.
In a preferred embodiment of the present invention, the gas emission material is hydrogenated alloy or a hydrogen occlusion material containing at least one selected from the group consisting of Zn, Ti, Ta, V, Mg and Th.